(1) Field of the Invention
The present invention relates to an optical film, and more particularly relates to an optical film applied in a side-emitting backlight module.
(2) Description of the Prior Art
The optical films, such as diffusion film and brightness enhancement film are commonly used in the side-emitting backlight module of the notebook or display to concentrate light and enhance brightness.
Referring to FIG. 1, a conventional side-emitting backlight module 100 includes an top diffusion film 110, an brightness enhancement film 120 for enhancing the brightness in an X-axis direction, a brightness enhancement film 130 for enhancing the brightness in a Y-axis direction, a lower diffusion film 140, a light guide plate 150, a reflector 160, a light source 170, a lamp holder 180 and an outer frame 190, in which the top diffusion film 110, the bottom diffusion film 140, the brightness enhancement films 120 and 130 and the light guide plate 150 are the core technology and cost.
As above mentioned, the side-emitting backlight module 100 has two brightness enhancement films 120 and 130. However, a substitute technology has been raised, called V-Cut.
Referring to FIG. 2, a backlight module 200 using V-Cut technology has a diffusion film 220, a reverse prism sheet 240 and a light guide plate 260. In the V-Cut technology, a microstructure (not shown) is directly fabricated on the upper or lower surface of the light guide plate 260, and the reverse prism sheet 240 with a face-down prism-like structure replaces the two brightness enhancement films 120 and 130 in FIG. 1
Referring to FIG. 2, the light exited from the light guide plate 260 generates total reflection in the prism-like structure located at the underside of the reverse prism sheet 240 when passing the reverse prism sheet 240, by which the light gets out upwards vertically from the reverse prism sheet 240 and then goes through the diffusion film 220, so as to get the effect of shielding the dot pattern and a predetermined diffusion angle. Compared to FIG. 1, the V-Cut technology does not need the brightness enhancement films 120 and 130, as well as the top diffusion film 110 and the bottom diffusion film 140, which saves the cost and lightens the backlight module 200.
However, the backlight module manufactures try their best to decrease the cost, the only way to decrease the cost is to simplify the backlight module by reducing the number of the optical films. The backlight module 200 in FIG. 2 has not integrate the reverse prism sheet 240 and the diffusion film 220 yet, which meant the cost and fabrication threshold still may be lowered.